This invention is directed to improved stabilized aqueous crosslinked polysiloxane dispersions blended with silicone or organic fluids to produce new materials with novel properties.
Cured silicone rubber powders have been made by first preparing a water-based emulsion of a curable silicone composition, then curing the composition to form a water based dispersion of cured silicone rubber powder by heating it to 80.degree. C. to effect crosslinking, and finally removing the water from the water-based dispersion to harvest the rubber. The disadvantage of this approach is that the initial water-based dispersion only contains about 35% silicone solids. The remaining 65% of water is removed through a spray drying process. Agglomeration occurs in the spray drying process resulting in rubber powder particle sizes larger than those occurring in the latex (the dispersion of the crosslinked rubber). So finally, a sieving procedure is carried out to remove certain particle sizes.
The advantage of our invention, in contrast, is that we have found unexpectedly, that the viscosity of a fluid can be modified with a silicone latex without removing the water from the silicone latex. This eliminates the heating, harvesting, and sieving procedures. This is possible because the silicone latex is provided as an extremely high internal phase ratio latex, that is, it contains a crosslinked or cured rubber phase up to 95%, with the remainder being the water continuous phase. It is quite unexpected that one could swell the individual silicone latex particles with a solvent in the presence of a water continuous phase.
This particular silicone latex represents several significant advances in the art. First, the process of making the dispersion is improved since the high solids gel phase provides for a higher shear and lower particle size distribution. Second, an advantage is that due to the high polymer solids content of the diluted gel (above 75%), the composition does not require thickeners or other rheology modifiers to achieve excellent handling characteristics. A third advantage is the versatility of the process, allowing mixing of silicone polymer, water, surfactant, and cure package (i.e., a catalyst, a crosslinker, or both, or a self catalytic crosslinker), in the manufacture of a high solids oil-in-water emulsion as a gel phase intermediate. The gel phase intermediate can be used immediately after preparation or stored. The high solids gel is then diluted with water to form a dispersion having greater than 75% silicone solids content. The gel can be further processed by adding additional ingredients, if desired, and diluting the dispersion to the desired solids content.